The present invention relates to the field of implantable medical devices, and, more particularly, to cardiac pacing systems that adapt the pacing rate by using two types of sensed information, for example from two different sensors, to determine the required heart rate and to adjust the pacing rate appropriately.
Implantable pulse generators (or IPGs) are well known in the art. Some of these devices provide pacing stimuli to the heart at a predetermined rate. The stimuli may be applied at a fixed rate, on demand, at a rate synchronized to atrial activity or at a rate synchronized to ventricular activity. This type of pacing function may also be used in other devices such as, for example, implantable cardioverter defibrillators (ICDs) or in external pacemakers. Most IPGs include sense amplifier circuitry for detecting intrinsic cardiac electrical activity. Some IPGs also include sensors to determine reliably the heart rate (or pacing rate) in a heart under different conditions.
This may occur, for example, when a sensor indicates a heart workload that is too high (a false positive). For example, a sensor may indicate high cardiac workload in a person when, in fact, the person is only sitting on a bus on a bumpy road, attending a particularly raucous concert or in another such shaky environment. On some occasions, brushing one""s teeth may induce movements in the upper body that may be inappropriately sensed as a high cardiac workload.
With a heart rate that is artificially increased to an inappropriately high rate, the conduction time to the ventricle may be prolonged. Although this is a normal electrophysiological phenomenon, it is of some concern that the conduction time may be overly prolonged, even to a level where conduction to the ventricle is blocked. Thus, it would be desirable to determine an appropriate rate of stimulation for any given conditions, e.g., the number of times per specific period that a stimulating pulse should be delivered for the desired response to be evoked under the given set of conditions. In particular, a rate of stimulation that produces a more physiological heart rate with a suitable conduction time to the ventricle would be desirable. Such a rate of stimulation would protect the heart from too prolonged a conduction time to the ventricle, and would help prevent blockage of conduction to the ventricle.
Thus, a need exists in the medical arts for evaluating the rate of activity at which a pacing pulse is administered and adjusting the rate if necessary.
Several methods have been proposed in the prior art for improving an implantable device""s ability to administer pacing pulses.
For example, U.S. Pat. No. 5,144,950 to Stoop et al., entitled xe2x80x9cRate Controlled Pacemaker System Using AR Interval for Rate Controlxe2x80x9d, hereby incorporated by reference in its entirety, discloses an AAIR rate responsive device that uses the measured A-R interval to control the rate response.
U.S. Pat. No. 4,856,524 to Baker, entitled xe2x80x9cA-V Responsive Rate Adaptive Pacemakerxe2x80x9d hereby incorporated by reference in its entirety, discloses an A-V responsive IPG where the pacing interval is based on one of two linear functions depending upon whether atrial activity is spontaneous or induced.
As discussed above, the most pertinent prior art patents are shown in the following table:
All the patents listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.
The present invention is therefore directed to providing a method and system for adapting the rate in a cardiac pacing system by using two different types of sensed information, for example, from two sensors, to determine the required heart rate and to adjust the pacing rate appropriately. Such a system of the present invention overcomes the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of determining the heart rate and adjusting the pacing rate appropriately.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the instantaneous stimulation of a mammalian heart. Those problems include, without limitation: the ability to adapt the rate of stimulation appropriately based on the activity of the heart.
In comparison to known techniques for adapting the rate of stimulation, various embodiments of the present invention may provide the following advantage, inter alia, i.e., the ability to adapt the rate of stimulation by using two types of sensed information, for example information from two sensors, to determine the required heart rate and to adjust the pacing rate appropriately based on the sensed information.
Some of the embodiments of the present invention include one or more of the following features: an implantable medical device including at least one sensing lead capable of sensing two types of sensed data or including two sensing leads, at least one pacing lead, a microprocessor and an input/output circuit including a digital controller/timer circuit, an output circuit, a sense amplifier, a peak sense and threshold measurement device, a comparator, an electrogram amplifier, a sensor for determining basic rate response and an additional sensor for measuring the electrical conduction time to the ventricle, for example by measuring the time from a sensed atrial signal to a sensed ventricular signal (PR interval) or by measuring the time from an atrial pacing pulse to a ventricular sensed signal (AR interval).
Furthermore, in accordance with the present invention, an embodiment for a method and system of adapting heart rate in cardiac tissue based on two types of sensed information, where one type is the electrical conduction time to the ventricle, is provided. A pulse is transmitted to the cardiac tissue. An activity signal is received. A first interval signal is also received and the pacing rate is adapted based on the first interval signal. A second interval signal is then received and the adapted pacing rate is verified using the second interval signal.